In their final debate before the June 26 primary, the four Democrats vying for a chance to become Colorado’s next governor tussled Monday evening over everything from immigration and guns, to the state’s rural divide and oil and gas drilling.

But the real fight came on the topic of campaign-trail tactics, where the candidates again picked one another apart over allegations of negative television ads and inappropriate campaign financing.

The bulk of those attacks were leveled at U.S. Rep. Jared Polis, D-Boulder, the presumptive front-runner, who has injected more than $11 million of his own money into the race.

The theme of “clean campaigns” and whether candidates’ broke their pledges to run them was the most contentious part of the debate and is an issue that has been swirling around the Democratic race for weeks. It’s become a sticking point at forums and fodder for candidates’ news releases as they jockey for votes.

Heading into the final stretch before the primary, it was clear during Monday’s debate hosted by The Denver Post, Denver7 and the University of Denver that the theme wasn’t waning.